Hybrid vehicles with an Internal Combustion Engine (ICE) include an exhaust gas treatment system for reducing the toxicity of the exhaust gas from the engine. The treatment system typically includes a catalytic converter unit, which includes a catalyst that reduces nitrogen oxides in the exhaust gas to nitrogen and carbon dioxide or water, as well as oxidizes carbon monoxide (CO) and unburnt hydrocarbons (HCs) to carbon dioxide and water. The catalyst may include, but is not limited to, Platinum Group Metals (PGM). The catalyst must be heated to a light-off temperature of the catalyst before the catalyst becomes operational. Accordingly, the exhaust gas must heat the catalyst to the light-off temperature before the reaction between the catalyst and the exhaust gas begins.
The hybrid vehicle may further include an electric motor. The internal combustion engine and the electric motor may each be selectively engaged to power the vehicle, i.e., the internal combustion engine and the electric motor may each be selectively engaged to generate a drive torque for a transmission. When the electric motor is being engaged to provide the drive torque to the transmission, the internal combustion engine is typically not being fueled and is not running. However, because both the electric motor and the internal combustion engine are coupled to the transmission to provide the drive torque to the transmission, the electric motor may cause the internal combustion engine to spin when the electric motor is engaged to provide the drive torque. Alternatively, the internal combustion engine may have to be spun in an un-fueled condition to provide additional drive torque if the driver requests it to allow more torque from the electric motor to go to the wheels. When the internal combustion engine is being spun while the electric motor is providing the drive torque, the internal combustion engine produces a flow of air which is directed through the exhaust gas treatment system. This flow of air collects hydrocarbons from the engine and conveys the hydrocarbons through the exhaust treatment system. Furthermore, this flow of air is not heated, and cools the components of the exhaust gas treatment system, including the catalyst. If the catalyst is cooled to a temperature below the light-off temperature, then the flow of air containing the hydrocarbons suspended therein may not be properly treated. Additionally, if the catalyst is cooled to a temperature below the light-off temperature then exhaust gas from the internal combustion engine, once fueled and running, may also not be properly treated.